The present invention relates generally to systems for transmitting synchronizing signals. More particularly, the invention relates to a synchronizing signal transmission system operating to mix a horizontal synchronizing signal and a vertical synchronizing signal for television signals, to transmit the synchronizing signal thus mixed with a single signal transmission line, and separating and restoring this mixed signal as a horizontal synchronizing signal and a vertical synchronizing signal.
Heretofore, systems as exemplified by the following examples have been known for transmitting a horizontal synchronizing signal and a vertical synchronizing signal by means of a single signal transmission line such as a coaxial cable and separating and reproducing the two synchronizing signals on the transmission receiving end.
1. A system wherein a composite synchronizing signal for standard television broadcasting is transmitted and is separated at the transmission receiving end as a horizontal synchronizing signal and a vertical synchronizing signal.
2. A system wherein a horizontal synchronizing signal and a vertical synchronizing signal are mixed directly as they are to produce a mixed synchronizing signal, which is transmitted to the receiving side, where it is differentiated and integrated thereby to separate and restore the same as a horizontal synchronizing signal and a vertical synchronizing signal.
The prior art system (1) has been accompanied by the difficulty of the need for using a complicated circuit for generating the composite synchronizing signal. Furthermore, in transmitting a synchronizing signal between a control unit and a television camera head, it is necessary to adjust the phase of the horizontal synchronizing signal in accordance with the length of the camera cable for connecting the control unit and the camera head. By the above mentioned known system, however, the phase adjustment of the horizontal synchronizing signal thereof becomes extremely complicated and is difficult.
By the latter known system (2), the horizontal synchronizing signal on the transmission end is transmitted by mere superimposition and mixing thereof as it is with the vertical synchronizing signal, and on the receiving end, the mixed synchronizing signal thus transmitted is differentiated to separate and restore the horizontal synchronizing signal and integrated to separate and restore the vertical synchronizing signal. Then, in order to cause the video signal to undergo interlaced scanning, in general, the phase relationship of the horizontal and vertical synchronizing signals differ in the even-number fields and the odd-number fields.
More specifically, in an even-number field, the rising part and falling part of the vertical synchronizing signal are between adjacent horizontal synchronizing signals, while in an odd-number field, the rising part and falling part of the vertical synchronizing signal are respectively coincident with those of the horizontal synchronizing signal. Then, since the vertical synchronizing signal is obtained by integrating the mixed synchronizing signal, the rising time of the separated and restored vertical synchronizing signal differs with every field, whereby it becomes impossible to accomplish a fully satisfactory interlaced scanning. Consquently, the vertical resolution decreases, and the picture quality deteriorates.